The objective of this study is to investigate and compare increments in plasma levels of pancreatic polypeptide (PP-an islet cell hormone) in response to the ingestion of a protein meal in three groups of members of the RW/MODY1 pedigree: 1) subjects with normal glucose tolerance who have a mutation of the HNF-4a/MODY1 gene for maturity-onset diabetes of the young, 2) subjects with normal glucose tolerance who are negative for the MODY1 gene, and 3) subjects with diabetes without or with mild fasting hyperglycemia who are MODY1 gene positive. Previous studies have suggested subnormal increments in plasma PP in response to insulin-induced hypoglycemia in groups of subjects who carry the MODY1 gene. The proposed studies should substantiate that PP cell function is defective in subjects with a mutation in the HNF-4a gene and if so, prove that the gene controls the function of PP cells, in addition to those of the b- and a- cells.